When I have this mod enabled no vehicles will spawn on highways meaning that no citizens can move to cities, no resources get delivered, etc. Disabling the mod fixes this.
I am using a list of mods recommended by the Youtuber City Planner Plays. The list can be found here https://steamcommunity.com/sharedfiles/filedetails/?id=2985784591. I have no mods beyond that and haven't done much to mess with their settings. It took ages of disabling each mod individually to find that RICO was the issue.
Sometimes when loading with RICO enabled I would get this error message:

Broken assets:

Road: Road Connection: Private building cannot have manual placement style [BrokenAssetException]

Details:
No details

Also, when zooming right to the end of highway connections before they enter the fog at the end of map there is symbols indicating that the highway needs water and power connections. These disappear when RICO is disabled.

I couldn't find anywhere else to post a bug report so if this isn't the right place then please someone point me in the right direction.